1 Field of the Invention
The present invention generally relates to a via structure, and more particularly to a device having a via structure wherein the via structure has a high aspect ratio by utilizing a positive-type photoresist layer.
2. Description of the Related Art
Components located on the active surface of a semiconductor device become smaller in size as the geometric shape of the semiconductor device becomes gradually smaller. For example, the passive component (e.g. a capacitor) is constituted by two metallic layers and one via hole. In order to decrease the volume of the capacitor, it is necessary to decrease the area of the metallic layers. Also, it is necessary to have a high aspect ratio for the via hole. A conventional method for manufacturing a device having via hole generally utilizes the photosensitive benzocyclobutene (BCB) to act as a low-k dielectric material layer. However, the size of the via hole is limited by the property of the negative-type photosensitive BCB when the via hole having a small size is formed by exposing and developing the photosensitive BCB.
Referring to FIG. 1, it depicts a conventional semiconductor device 10. The semiconductor device 10 includes a silicon substrate 12, a plurality of metallic traces 16 and a low-k dielectric material layer 30 (photosensitive BCB). The silicon substrate 12 is provided with a plurality of pads 15 for electrically connecting to an integrated circuit (IC) (not shown) located on the active surface. The metallic traces 16 are disposed on the silicon substrate 12 and electrically connected to the pads 15. The dielectric material layer 30 (photosensitive BCB) is patterned by exposing and developing processes, thereby defining through holes 20. Metallic material 22 is formed in each through hole 20 so as to form a via hole 24 located on the metallic traces 16. The dielectric material layer 30 (photosensitive BCB) is made of a negative-type polymer material, and thus the resolution is not good when the through hole 20 is formed by exposing and developing the dielectric material layer 30 (photosensitive BCB). The through hole 20 formed in the dielectric material layer 30 of photosensitive BCB has an upper opening and a lower opening wherein the hole diameter of the upper opening is wider than that of the lower opening. Thus, the size of the via hole 24 cannot be very small. For example, considering the photosensitive BCB having a thickness t1 of 5 μm, the through hole 20 formed generally has a hole diameter d1 of 30 μm at most. Thus, the aspect ratio (the ratio of depth D1 to width W1) of the via hole 24 must be limited to less than 0.167. Also, when a small-sized via hole 24 is formed in the dielectric material layer 30 (photosensitive BCB) by the exposing and developing processes, it is easy to leave some residual BCB in the via hole 24, which is hard to remove. Thus, manufacturing and electrical problems tend to rise in the subsequent processes.
U.S. Patent Publication Number 2004/0077174, entitled “Method for forming a high aspect ratio via”, discloses a method for manufacturing via holes. Although this patent discloses the method for manufacturing via holes having high aspect ratios, this patent fails to disclose that the via holes are formed by utilizing a positive-type photoresist layer, wherein the via holes are located in the low-k dielectric material layer and have high aspect ratios, being more than 0.167.
Accordingly, there exists a need for a device having a via structure capable of solving the above-mentioned problems.